1. Field of the Invention
The present invention relates to a balancer-fitting configuration for an internal combustion engine.
2. Description of Background Art
The cylinders of some known internal combustion engines are inclined forward and paired balancers, one above and the other below the crankshaft, are disposed within the maximum width of the locus of the crank weight in the longitudinal direction of the vehicle which is fitted with the internal combustion engine. For example, Japanese Unexamined Patent Publication No. 10-73148 discloses such an internal combustion engine.
As shown in FIG. 10 of the present invention, the internal combustion engine 01 disclosed in the above patent publication has a cylinder 02 which is inclined a little forward and balancers 04 and 05 which are disposed generally above and below a crankshaft 03, within the maximum width of the locus of the crank weight of the crankshaft 03 in the longitudinal direction of the vehicle which is fitted with the internal combustion engine 01. Thus, the length of the internal combustion engine in the longitudinal direction of the vehicle is decreased in size.
Because the cylinder axial line C-Cxe2x80x2 is inclined only a little forward, the balancers 04 and 05 disposed generally above and below the crankshaft 03 are not positioned symmetrically in relation to the cylinder axial line C-Cxe2x80x2.
Accordingly, the rotation of the upper and lower balancers 04 and 05 acts, as a moment, on the crankshaft 03 to become an additional factor of vibration.
In the case of the above patent publication, to rotate the upper balancer 04, an idler gear 06 is located between the crankshaft 03 and the balancer 04. Thus, the rotation of the crankshaft 03 is transmitted through the idler gear 06 to the upper balancer 04 to rotate it in the same direction as the crankshaft 03.
Because the idler gear 06 is disposed between the crankshaft 03 and the upper balancer 04 and protruding backward relatively to them, the part of the crankcase behind the crankshaft 03 is bulky. Accordingly, the rear wheel has to be disposed more backward to avoid the interference between the crankcase and the rear wheel, making the frame large.
The present invention was made in view of the above problem. Accordingly, an object of the present invention is to provide a balancer-fitting configuration for an internal combustion engine. With the balancer-fitting configuration of the present invention: (i) the vibration control of an internal combustion engine with forward-inclined cylinders is achieved effectively by using paired balancers separated and disposed opposite to each other; (ii) the part of the crankcase behind the crankshaft is decreased in the longitudinal direction of the frame; and (iii) a space within which the real wheel swings is obtained without enlarging the frame.
To achieve the above object, in accordance with a first aspect of the present invention, there is provided a balancer-fitting configuration for an internal combustion engine with a crankcase, a crankshaft, and a crank weight for a vehicle with a rear wheel disposed close to the rear of the crankcase, wherein: (i) the cylinder axial line of the internal combustion engine is inclined generally horizontally, and paired balancers, one above and the other below the crankshaft, are disposed generally within the maximum width of the locus of the crank weight in the longitudinal direction of the vehicle; and (ii) a starter is disposed in the vicinity of the upper balancer, and accessories such as an oil pump are disposed in the vicinity of the lower balancer.
Because the cylinder axial line is inclined generally horizontally and paired balancers, one above and the other below the crankshaft, are disposed generally within the maximum width of the locus of the crank weight in the longitudinal direction of the vehicle, the balancers can be positioned symmetrically in relation to the cylinder axial line, with the crankshaft being the center between the balancers.
Accordingly, the rotation of the upper and lower balancers does not cause a moment to the crankshaft. Accordingly, vibration can be effectively controlled with the paired balancers separated from each other without being concerned about an additional factor effecting vibration.
Because the paired balancers are within the maximum width of the locus of the crank weight in the longitudinal direction of the vehicle, the part of the crankcase behind the crankshaft can be decreased in size in the same direction. In addition, the starter and the oil pump are disposed in the vicinity of the balancers. Thus, the length of the internal combustion engine including the starter and the oil pump can be decreased in size, and a space in which the rear wheel swings behind the crankcase can be obtained without enlarging the frame.
In accordance with a second aspect of the present invention, there is provided a balancer-fitting configuration of an internal combustion engine as in the first aspect of the present invention, wherein the shaft of the upper balancer is disposed behind the crankshaft and the starter is disposed before the upper balancer shaft.
Because the starter is disposed before the upper balancer shaft which is disposed behind the crankshaft, the starter does not excessively protrude upward. In addition, because the starter is positioned within the maximum width of the locus of the crank weight in the longitudinal direction of the vehicle, the starter does not protrude forward. Thus, the internal combustion engine can be made compact.
In accordance with a third aspect of the present invention, there is provided a balancer-fitting configuration of an internal combustion engine as in the first aspect of the present invention, wherein the accessories such as an oil pump are disposed before the shaft of the lower balancer.
Because the accessories are disposed before the lower balancer shaft, the accessories do not affect the ground clearance of the frame.
In accordance with a fourth aspect of the present invention, there is provided a balancer-fitting configuration for an internal combustion engine as in any of the first through third aspects of the present invention, wherein the rear wheel which is disposed close to the rear of the crankcase is journaled on an axle at the rear end of an arm which swings about a shaft in axial alignment with the crankshaft.
An internal combustion engine with cylinders inclined generally horizontally tends to be long. However, the distance from the internal combustion engine to the rear wheel can be shortened by configuring the crankshaft and the arm supporting the rear wheel at its rear end so that the arm can swing about a shaft in axial alignment with the crankshaft. Thus, the frame can be made small in length.
In accordance with a fifth aspect of the present invention, there is provided a balancer-fitting configuration for an internal combustion engine comprising: a crankcase; a crankshaft; and a balancer which has a shaft parallel to the crankshaft, wherein (i) a driving gear fitted on the crankshaft and a balancer driven gear fitted on the balancer shaft engage with each other to transmit motive power; (ii) the balancer driven gear is a scissors gear comprising two spur gears which are put together side by side and urged to slip out of the exactly overlapping state of the tooth profiles of one spur gear and those of the other; and (iii) a positioning pin fixes the two spur gears of the balancer driven gear in the exactly overlapping state of the tooth profiles of one spur gear and those of the other and positions the balancer driven gear with respect to the crankcase.
Because the balancer driven gear is a scissors gear, the rotation is transmitted smoothly.
Because the positioning pin fixes the two spur gears in the exactly overlapping state of the tooth profiles of one spur gear and those of the other and positions the balancer driven gear with respect to the crankcase, the phase matching of the balancer can easily be made when it is built in the internal combustion engine. Thus, the assembling efficiency is raised significantly.
In accordance with a sixth aspect of the present invention, there is provided a balancer-fitting configuration of an internal combustion engine as in the fifth aspect of the present invention, wherein (i) a through hole is made at a position on the crankcase corresponding to the position of the positioning pin and (ii) the positioning pin can be removed through the through hole.
Because the positioning pin can be removed through the through hole of the crankcase after the balancer is built in the internal combustion engine, the assembling efficiency is high.
In addition, a worker can be prevented from forgetting to remove the positioning pin after building it in the internal combustion engine by configuring the positioning pin so that it checks the rotation of the internal combustion engine unless it is removed.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.